Hi everyone, I am currently renovating my first 1950's property and I have just had two chimney breast openings widened, one to fit a range cooker and the other to fit a new electric fire. Since having them widened the floor is now not level with the floor boards. In the opening there is a mixture of rubble and concrete base. I'm not sure what to use to bring up up to level, concrete or self levelling compound? The deepest part is approx 80mm from the top of the floor board down to the rubble.